In-Situ Free-Space Dielectric Testing of Unclad Substrates
Non-destructive free-space characterization evaluates bulk dielectric properties of raw unclad laminates without etched coupon waste or copper interface errors.
Free Space Calibration
Measurement Compensation
Reference measurements performed in an empty transmission path establish the baseline for non-contact electromagnetic characterization of dielectric materials. This process of free space calibration removes the systematic errors introduced by coaxial cables, horn antennas, and test fixtures before a sample is inserted. By characterizing the propagation channel without the material under test, the analyzer isolates the true reflection and transmission coefficients of the slab.
Mathematical Correction
Mathematical algorithms process the baseline signals to calculate the scattering parameters of the empty path. To execute a free space calibration, operators usually perform thru, reflect, and line steps in the open air. This sequence establishes the phase reference planes at the boundary of the material holder.
System drift caused by thermal expansion or cable movement during subsequent test runs requires a recalibration to maintain measurement precision.
Operational Procedure
Precise physical alignment of the antennas ensures the validity of the gathered calibration data. Horn antennas must be positioned in the far-field region to generate planar wavefronts at the material plane. Any deviation in the spacing or parallelism of the antennas alters the propagation path, which invalidates the free space calibration.
Ensuring a clear keep-out zone around the propagation path prevents stray reflections from bench equipment or laboratory walls from corrupting the measurement. This structural control allows the system to determine the material properties with high repeatability.